health_and_medicinefandomcom-20200213-history
Tobacco use disorder
Tobacco use disorder is a behavioural disorder associated with tobacco use, and is usually an addiction to nicotine and other psychoactive constituents of tobacco. __TOC__ Mechanism The mechanism of action of nicotine is discussed here. In summary, however, nicotine being a nicotinic acetylcholine receptor full agonist for most subunits, increases cholinergic tone in much of the central nervous system, but especially in the mesolimbic pathway, where its α4β2 and α6β2 subunits predominate. This property enables it induce the release of dopamine into the synaptic cleft, producing euphoria. This euphoria is an automatic reward for drug use that causes repeated use of the drug, until epigenetic changes occur in the individuals brain that cause an addiction. Amongst these changes, include an upregulation of ΔFosB, a transcription factor and inhibition of histone deacetylase activity. Causes Several risk factors for addiction to nicotine have been uncovered, many of them are genetic. It is estimated that about 20-80% of one's odds to start smoking can be directly attributed to genetic factors. Despite this smoking is highly addictive and smokers are twice as likely as cocaine users (via snuffing the powder) to develop an addiction upon first exposure to their respective drug of abuse. People with''' psychiatric disorders', namely '''severe depression', schizophrenia or bipolar disorder are also significantly more likely to become addicted to cigarette smoking, which may be partly due to a self-medicating behaviour as nicotine can sometimes help with some of their symptoms. For example, in 2000, some 20-30% of the general population and 26-90% of the psychiatric population (dependent on the specific mental illness in consideration) smoked tobacco. Overall the more pleasurable you find smoking, the more likely it is you will become addicted. The genes that are implicated in influencing one's propensity for smoking include the genes involved in the metabolism of nicotine, the genes involved in the creation of the receptor proteins for the and the genes involved in the monoaminergic responses to nicotine consumption. Withdrawal Withdrawal is characterized by: irritability, anxiety, depression, restlessness, poor concentration, increased appetite, weight gain and insomnia. Weight gain is probably the biggest deterrent from quitting; on average quitting smoking is associated with weight gain of 5 kg in the first year and 6-7 kg overall. But it is worth noting that bupropion and is known to cause some weight loss, in fact, in the U.S. a combination product containing bupropion and phentermine is now approved for the short-term management of obesity. One possible treatment if weight gain is particularly an issue is long-term NRT, even after one has successfully quit smoking. Treatment Non-drug approaches Behavioural modification therapy, a type of talk therapy can improve (albeit slightly) the rate of successful smoking cessation, along with the drug treatments highlighted in the next paragraph. In the pregnant population it is usually pursued as a first-line treatment. Second-line treatment in pregnant women consists of . The talking approach is considered particularly helpful in those smokers with depression. Drug-based approaches There are three cornerstones of drug therapy for nicotine dependence: nicotine replacement therapy (NRT; such as nicotine gum, nasal sprays and patches, e-cigarettes), bupropion and varenicline. Simply talking to one's physician or pharmacist also increases one's odds of successfully quitting. NRT is usually preferred as it is usually the best combination of safe and effective; it is also available without requiring a prescription in most countries. The major side effects of NRT, include: burning of the mouth and throat, nausea/vomiting (dose-related), increased salivation (that is, producing more saliva than more, which can make you drool), abdominal pain, vomiting, diarrhoea, dizziness, weakness, high blood pressure that is followed by low blood pressure, mental confusion, cold/flu-like symptoms, palpitations, sleep disturbances, vivid dreaming, muscle aches and/or pains, chest pain, anxiety, irritability, sleepiness, menstrual changes, allergic reactions, localized reactions, headache, hearing and visual disturbances, shortness of breath, faintness or seizures. Heart rhythm anomalies may also occur. Localized reactions are basically things that occur near where the nicotine enters the body, such as skin rashes, nasal congestion, etc. Bupropion, is a noradrenaline-dopamine reuptake inhibitor, hence potentially “taking the edge off” the withdrawals, whilst simultaneously blocking the nAChRs, hence preventing the pleasurable effects of smoking. It is particularly helpful in patients that smoke as a means of self-medicating their depression. The only real problem with it are rare side effects (occurring in fewer than 1% of patients receiving the drug) of seizures (rarely life-threatening; seizures occur in fewer than 0.4% of patients that take it) and anaphylaxis. It may be particularly helpful in smokers with depression or anxiety, as it is also used (albeit rarely, in Australia or the U.K.) to treat depression. Must be dosed two times a day, in Australia and the U.K., can be dosed once a day in the United States, however (see the bupropion page for why). Varenicline, on the other hand, is a partial agonist at the nAChRs, hence serving two functions, firstly it blocks the pleasurable effects of smoking whilst simultaneously attenuating the symptoms of nicotine withdrawal. Varenicline is believed to be superior to bupropion in as far as the % of people that use it that successfully quit smoking. People receiving varenicline are 2.9 times more likely to succeed in their efforts to quit smoking, whereas those on bupropion are 1.7 times more likely to succeed and those on NRT are 1.6 times more likely to succeed. Many physicians will try to avoid giving their patients varenicline as it can cause depression (in fewer than 10% of people that take it) and, rarely, suicidal thoughts. Cytisine may also be used for smoking cessation; although it is not available for this use in any English-speaking country I am aware of (including Australia, Canada, Hong Kong, the United Kingdom, United States or Singapore). Less commonly used, yet still supported by the evidence, treatments include: * Clonidine. Dose-limiting side effects of sedation and orthostatic hypotension . * Nortriptyline. A tricyclic antidepressant that serves, predominantly, as a noradrenaline reuptake inhibitor (NRI); seldom used for this purpose nowadays due to side effects such as urinary retention. * Topiramate. Only one clinical trial supports this use. * Rimonabant may also be used but the evidence as to whether it aids smoking cessation in the long-term is inconclusive. It has been withdrawn from the market in most developed countries amidst concerns over increased suicidality in patients treated with it. Special populations Several specific populations '''are particularly at risk of experiencing tobacco-related harm of they smoke or inhale second-hand smoke. These populations include pregnant or nursing women, children and those with pre-existing conditions like cancer, mental disorders or heart/lung disease. Pregnancy and lactation Pregnant women are advised to avoid exposure to tobacco smoking, both first-hand (that is, from them smoking) and second-hand. The '''complications of smoke exposure during pregnancy include: low birth weight, miscarriage (rate increased by about 10-20%), preterm labour, birth defects (including heart defects, digestive defects, facial defects, etc.; usually by about 10-50%, depending on specific defect), behavioural disorders like attention-deficit/hyperactivity disorder, conduct disorder and sudden infant death syndrome (SIDS). Smoking in this population also seems to come with a racial predilection in Australia: Aboriginals/Torres Strait Islanders are three times more likely to smoke while pregnant than the general population. Second-hand smoke exposure in pregnant women is known to increase the risk of low birth rate. Children Smoking in children, luckily, thanks to hard-hitting advertisements of the risk has been on the decrease. Despite this about 80% of all new smokers in Australia are children or adolescents. Passive smoke exposure (that is, second-hand smoke) may stunt growth in children. Likewise, passive smoke exposure in children may increase their risk of , lower respiratory tract infections (like pneumonia), impair lung function and increase their risk of middle ear disease. People with heart or lung disease Smoking in these populations seems to accelerate the progression of their disease, and while there was some concern that perhaps smoking cessation aids like , bupropion or varenicline could also accelerate the progression of the disease, the general consensus of opinion is that smoking cessation should take priority over everything else, including any theoretical risk for exacerbating these pre-existing conditions. Cancer patients Those with cancer are advised to limit their exposure to cigarette smoke as it can cause some pharmacokinetic interactions with their chemotherapeutic agents, likewise it could accelerate the progression of their cancer, this is likely due to a combination of factors, including increased angiogenesis, modified cancer cell survival, etc. Fortunately, however, quitting smoke does seem to improve survival in lung cancer patients. The mentally ill Tobacco is abused amongst those with mental disorders significantly more frequently than by the general population, approximately 70-80% of schizophrenics are smokers, compared to less than 20% for the general population. It is believed that this might be due to a sub-conscious desire to self-medicate themselves, as nicotine is known to improve cognition and some other symptoms of schizophrenia. It may also attenuate some of the side effects of antipsychotic medications. Likewise nicotine is known to relieve anxiety in most smokers. Despite this, it has been found that quitting smoking improves various aspects of mental health, including in the mentally ill. Studies have found that smoking is associated with a two-fold increase in risk for depression in the future. Its association with anxiety disorders is less clear. Benefits from quitting In eight hours almost all the excess carbon monoxide in a smoker's body is absent, in five days most of the excess nicotine is out of the body, in one week one's sense of smell and taste improves, in twelve weeks one's lungs regain the ability to clean themselves, at three months one's lung function improves by 30%, at twelve months one's risk of heart disease halves and if one is an Australian your wallet would have gained over $4,500 and in five years one's risk of stroke returns to normal. Notes Reference list Category:Drug addiction Category:Nicotine